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Stages of Sleep

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Stages of Sleep
144
Chapter 4 Consciousness
due to an eye disorder may be ashamed to seek the medical help they need to solve the
problem (Menon et al., 2003). If mental patients hallucinate, they often feel stress and selfblame and may choose not to report their hallucinations. Those who do report them tend
to be considered more disturbed and may receive more drastic treatments than patients
who keep their hallucinations to themselves (Wilson et al., 1996). Among the Moche of
Peru, however, hallucinations have a culturally approved place. When someone experiences illness or misfortune, a healer conducts an elaborate ritual to find causes and treatments. During the ceremony, the healer takes mescaline, a drug that causes hallucinations.
These hallucinations are thought to give the healer spiritual insight into the patient’s problems (de Rios, 1989). In many other tribal cultures, too, purposeful hallucinations are
respected, not rejected (Grob & Dobkin de Rios, 1992).
In other words, states of consciousness differ not only in their characteristics but also
in their value to members of particular cultures. In the sections that follow, we describe
some of the most interesting altered states of consciousness, beginning with the most
common one: sleep.
Sleeping and Dreaming
䉴 Does your brain go to sleep when you do?
According to ancient myths, sleepers lose control of their minds and flirt with death as
their souls wander freely. Early researchers thought sleep was a time of mental inactivity, but sleep is actually an active, complex state (Hobson, 2005).
Stages of Sleep
LINKAGES
Does the brain shut down
when we sleep? (a link to
Biology and Behavior)
Online Study Center
Improve Your Grade
Tutorial: EEG and Different Stages off Sleep
slow-wave sleep Sleep stages 3 and 4,
which are accompanied by slow, deep
breathing; a calm, regular heartbeat;
and reduced blood pressure.
rapid eye movement (REM) sleep The
stage of sleep during which the EEG resembles that of someone who is awake,
but muscle tone decreases dramatically.
Sleep researchers study the brain’s electrical activity during sleep by taping tiny discs
to a person’s scalp and connecting them to an electroencephalograph, or EEG. The resulting EEG recordings, often called brain waves, vary in height (amplitude) and speed (frequency) as behavior or mental processes change. The brain waves of an awake, alert
person are irregular, small, and closely spaced; that is, high frequency and low amplitude. A relaxed person with closed eyes shows more rhythmic brain waves occurring at
slower speeds, about eight to twelve cycles per second (cps). During a normal night’s
sleep, your brain waves show distinctive and systematic changes in amplitude and frequency as you pass through various stages of sleep (Durka et al., 2005).
Slow-Wave Sleep Imagine that you are participating in a sleep study. You are
hooked up to an EEG and various monitors, and a video camera watches as you sleep
through the night. If you were to view the results, here’s what you’d see: At first, you
are relaxed, with eyes closed, but awake. At this point, your muscle tone and eye movements are normal, and your EEG shows the slow brain waves associated with relaxation. Then, as you drift into sleep, your breathing deepens, your heartbeat slows, and
your blood pressure falls. Over the next half hour, you descend through four stages of
sleep that are characterized by even slower brain waves with even higher amplitude (see
Figure 4.3). The last two of these, stages 3 and 4, are called slow-wave sleep. When
you reach stage 4, the deepest stage of slow-wave sleep, it is quite difficult to be awakened. If you were roused from this stage of deep sleep, you would be groggy and
confused.
REM Sleep After thirty to forty-five minutes in stage 4, you quickly return to stage
2 and then enter a special stage in which your eyes move rapidly under your closed
eyelids. This is called rapid eye movement (REM) sleep, or paradoxical sleep. It is
called paradoxical because its characteristics contain a paradox, or contradiction. In
REM sleep, your EEG resembles that of an awake, alert person, and your physiological
145
Sleeping and Dreaming
FIGURE
4.3
Awake (resting)
EEG During Sleep
EEG recordings of brain wave activity
show four relatively distinct stages of
sleep. Notice the regular patterns of brain
waves that occur just before a person
goes to sleep, followed by the slowing of
brain waves as sleep becomes deeper
(stages 1 through 4). In REM (rapid eye
movement) sleep, the frequency of brain
waves increases dramatically. In some
ways the brain waves of REM sleep resemble patterns seen in people who are
awake.
Stage 1 sleep
Stage 2 sleep
Stage 3 sleep
Stage 4 sleep
REM sleep
Seconds
Source: Horne (1988).
arousal—heart rate, breathing, and blood pressure—is also similar to when you are
awake. However, your muscles are nearly paralyzed. Sudden, twitchy spasms appear,
especially in your face and hands, but your brain actively suppresses other movements
(Blumberg & Lucas, 1994). In other words, there are two distinctly different types of
sleep, REM sleep and non-REM, or NREM, sleep. (Lu el al., 2006
Most people pass through the cycle of sleep stages four to six times
each night. Each cycle lasts about ninety minutes, but with a somewhat changing pattern of stages and stage duration. Early in the night, most of the time is spent in slowwave sleep, with only a few minutes in REM (see Figure 4.4). As sleep continues,
though, it is dominated by stage 2 and REM sleep, from which sleepers finally awaken.
Sleep patterns change with age. The average infant sleeps about sixteen hours a day.
The average seventy-year-old sleeps only about six hours (Roffwarg, Muzio, & Dement,
1966), and elderly people tend to wake more often during the night than younger people do (Floyd, 2002). The composition of sleep changes, too. REM accounts for half
of total sleep in newborns but less than 25 percent in young adults. Individuals vary
widely from these averages, though. Some people feel well rested after four hours of
sleep, whereas others of similar age require ten hours to feel satisfied (Clausen, Sersen,
& Lidsky, 1974). To some extent, too, sleep patterns are a matter of choice or necessity. For example, North American college students get less sleep than other people
their age (Hicks, Fernandez, & Pellegrini, 2001). This trend has grown over the last
thirty years as students deal with academic and job responsibilities, along with family
obligations and a variety of social and recreational activities—including those latenight sessions playing computer games or surfing the Internet. You have probably
noticed the results of sleep deprivation as your classmates (or you?) struggle to stay
awake during lectures.
A Night’s Sleep
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